1. Field of the Invention
The present invention relates to a fluid control apparatus for an endoscope, the fluid control apparatus being provided on an endoscope and switching between supply of a gas to and suction of a fluid from an inside of a subject.
2. Description of the Related Art
In recent years, endoscopes have been widely used in a medical field. Endoscopes used in the medical field each enable an organ in a body cavity, which is a subject, to be observed by inserting an elongated insertion portion into the subject. Also, as necessary, various treatments can be performed using a treatment instrument inserted inside a treatment instrument insertion channel included in the endoscope.
Also, a configuration in which in addition to the aforementioned insertion channel, e.g., a forward water feeding duct for supplying a liquid to an inside of a subject and a gas/water feeding duct that feeds a liquid or a gas to an objective lens provided in a distal end face of a distal end in an insertion direction (hereinafter simply referred to as “distal end”) of an insertion portion are provided in an endoscope is known. A configuration in which the insertion channel is used as a suction duct for sucking a fluid such as a liquid, which is, e.g., a body fluid, or a gas in a subject is also known.
Furthermore, in order to achieve reduction in diameter of the insertion portion, an endoscope configuration in which only one duct is provided in an endoscope to feed a gas to an inside of a subject or suck a fluid from the inside of the subject using the one endoscope duct is known. As examples of endoscopes whose insertion portion has a very small diameter, endoscopes used in the otorhinolaryngological field are known.
Japanese Patent No. 4608606 discloses a configuration in which one endoscope duct is provided in an insertion portion and an operation portion provided so as to be continuous with the insertion portion at a proximal end in an insertion direction (hereinafter simply referred to as “proximal end”) of the insertion portion and a fluid control apparatus that switches between feeding of a gas to an inside of a subject or suction of a fluid from the inside of the subject using the one endoscope duct is provided on the operation portion.
FIG. 9 is a partial cross-sectional diagram schematically illustrating a conventional fluid control apparatus together with a gas feeding apparatus, a suction apparatus and an endoscope duct. Also, FIG. 10 is a cross-sectional diagram schematically illustrating a state in which a gas is supplied from the gas feeding apparatus in FIG. 9 using a gas feeding duct and the endoscope duct, according to switching control performed by the fluid control apparatus. Furthermore, FIG. 11 is a cross-sectional diagram schematically illustrating a state in which a fluid is sucked by the suction apparatus in FIG. 9 using a suction duct and the endoscope duct, according to switching control performed in the fluid control apparatus.
More specifically, as illustrated in FIG. 9, in Japanese Patent No. 4608606, a fluid control apparatus 500 provided on an operation portion of an endoscope includes a piston 501 including a gas feeding fitting 511, and a syringe 502 including a suction fitting 512. Also, the fluid control apparatus 500 includes an elastic member 503 including a suction leak hole 503h, and a button member 504.
A gas feeding apparatus 543 is connected to the gas feeding fitting 511 via a gas feeding tube 521. Note that a flow passage 501i inside the piston 501, a flow passage 511i inside the gas feeding fitting 511 and a flow passage 521i inside the gas feeding tube 521 communicate with a flow passage 505i of an endoscope duct 505 provided in an insertion portion and the operation portion of the endoscope.
Also, the flow passage 501i and the flow passage 511i provide a flow passage K of a gas feeding duct L in the fluid control apparatus 500, which supplies a gas A fed from the gas feeding apparatus 543 to the inside of the subject. In other words, the piston 510 and the gas feeding fitting 511 provide the gas feeding duct L in the fluid control apparatus 500.
In the flow passage 501i, a first valve 551 that closes the flow passage 501i when the fluid control apparatus 500 is not operated and a second valve 552 that opens the flow passage 501i are provided.
The first valve 551 functions as a check valve that prevents reverse flow of a fluid R to a part of the flow passage K on the upstream side relative to the first valve 551, and as illustrated in FIG. 10, is configured so as to open the flow passage K only when the gas A is fed from the gas feeding apparatus 543.
The second valve 552 is fixed to the piston 501 and formed integrally with a button member 504 exposed at an outer surface of the fluid control apparatus 500.
Also, as illustrated in FIG. 11, the second valve 552 is configured so as to, when suction from the inside of the subject is underway, close the flow passage 501i upon the second valve 552 being depressed by an operator together with the button member 504.
Also, the second valve 552 is configured so as to close the suction leak hole 503h upon the second valve 552 being depressed by the operator. Furthermore, the second valve 552 has a function that pushes the piston 501 down, thereby bringing the flow passage 505i and a flow passage V of a suction duct, which will be described later, into communication with each other.
Also, as illustrated in FIG. 9, a suction apparatus 533 is connected to the suction fitting 512 via a suction tube 522. Note that a flow passage 512i inside the suction fitting 512 communicates with a flow passage 522i of the suction tube 522 and is included in the flow passage V of the suction duct in the fluid control apparatus 500.
The syringe 502 covers an outer periphery of the distal end side in an extension direction Z of the piston 501 with a gap from the outer periphery, and in the gap, a flow passage 502i included in the flow passage V in the fluid control apparatus 500, which communicates with the flow passages 512i and 522i, is formed.
In other words, the syringe 502 and the suction fitting 512 provide a suction duct W in the fluid control apparatus 500.
Note that when the fluid control apparatus 500 is not operated, the flow passage V is occluded by a region provided at the distal end of the piston 501 and thereby is not in communication with the flow passage 505i, but in communication with an outside of the fluid control apparatus 500 via the suction leak hole 503h of the elastic member 503. Also, as stated above, the flow passage V communicates with the flow passage 505i only when the second valve 552 is pushed down.
According to the above, first, when the gas A is supplied to the inside of the subject using the flow passage K, the gas feeding apparatus 543 is driven, and then the gas A is introduced from the gas feeding apparatus 543 to the flow passage 511i via the flow passage 521i. Subsequently, as illustrated in FIG. 10, the gas A brings the first valve 551 into an open state from a closed state. Subsequently, the gas A is introduced to the flow passage 501i and supplied to the inside of the subject via the flow passage 505i. 
Note that in this case, even if the suction apparatus 533 is driven, the flow passage V is not in communication with the flow passage 505i but is in communication with the outside of the fluid control apparatus 500 via the suction leak hole 503h. Therefore, the suction apparatus 533 sucks atmospheric air T via the suction leak hole 503h and the flow passage V.
Next, when a fluid R in the subject is sucked using the flow passage 505i and the flow passage V, as illustrated in FIG. 11, the second valve 552 is pushed down together with the button member 504, whereby the flow passage 501i and the suction leak hole 503h are closed and the piston 501 is pushed down via the second valve 552.
Consequently, the flow passage V comes into a non-communication state with the outside of the fluid control apparatus 500 but comes into communication with the flow passage 505i, and thus, the fluid R in the subject is introduced from the flow passage 505i to the flow passage 502i. Subsequently, the fluid R is sucked to the suction apparatus 533 via the flow passages 512i and 522i. 
In this case, the flow passage 501i is closed by the first valve 551 and the second valve 552, whereby the fluid R in the subject and parts of the flow passages 501i and 505i on the downstream side relative to the second valve 552 is prevented from reversely flowing to the upstream side relative to the second valve 552 via the flow passage K.
In the configuration of the fluid control apparatus 500 disclosed in Japanese Patent No. 4608606, during use of the endoscope with neither gas feeding nor suction performed, in the flow passage K and the flow passage 505i, a pressure in the part on the downstream side relative to the first valve may vary, more specifically, the pressure may decrease for some reason.
A specific example will be indicated below with reference to FIGS. 12 to 14. FIG. 12 is a cross-sectional diagram illustrating a state in which a fluid supply member is connected to a liquid feeding fitting that communicates with the endoscope duct in FIG. 9 and a liquid is fed to the flow passage of the endoscope duct. Also, FIG. 13 is a cross-sectional diagram illustrating a state in which the liquid supplied from the fluid supply member to the endoscope duct in FIG. 12 is switched to a gas and the first valve is thereby opened. Furthermore, FIG. 14 is a cross-sectional diagram illustrating a state in which the supply of the gas from the fluid supply member in FIG. 13 causes a fluid in the gas feeding duct to reversely flow to the upstream side relative to the first valve.
Here, the configuration of the fluid control apparatus disclosed in Japanese Patent No. 4608606 includes no configuration that supplies a liquid to the inside of the subject via the flow passage 505i. Therefore, when a liquid is supplied to the inside of the subject, as illustrated in FIG. 12, it can be contemplated that a liquid E is supplied using a syringe 590, which is a fluid supply member, via a fitting 530 that is provided in the operation portion and is in communication with the flow passage 505i. 
Note that in the supply of the liquid E, as illustrated in FIG. 12, the liquid E and a fluid R containing a gas A remaining in the flow passage 501i reversely flow to the upstream side in the flow passage 501i. Here, the first valve 551 prevents the fluid R from reversely flowing to the upstream side relative to the first valve 551. Furthermore, with the liquid supply from the syringe 590, a pressure in the flow passage 501i increases, and the increase reaches a position just before the first valve 551.
However, since not only the liquid E but also a certain amount of the gas A are included in the syringe 590, as illustrated in FIG. 13, immediately after supply of all the liquid E in the syringe 590, the gas A in the syringe 590 is supplied to the flow passage 505i. 
In this case, at the moment of change from the supply of the liquid E to the supply of the gas A, the pressure on the downstream side relative to the first valve 551 in the flow passages 505i and 501i decreases because of a difference in pressure between the liquid E and the gas A. Accordingly, with the pressure decrease, as illustrated in FIG. 13, the first valve 551 is unexpectedly opened and the gas A in the flow passage 511i enters the flow passage 501i. 
Note that in this case, as a result of the decrease of the pressure in the flow passage 501i, the second valve 552 is pulled so as to close the flow passage 501i, but is prevented from closing the flow passage 501i by the gas A entered from the flow passage 511i. Therefore, the gas A enters the part of the flow passage 501i on the downstream side relative to the second valve 552.
Subsequently, as illustrated in FIG. 14, if the supply of the gas A from the syringe 590 to the flow passage 505i is continued, the pressure in the flow passage 501i increases again, whereby the first valve 551 operates to close the flow passage 501i. However, before the first valve 551 is completely closed, the fluid R remaining in the flow passages 501i and 505i reversely flows because of the pressure increase. As a result, the fluid R reversely flows to the upstream side relative to the first valve 551, that is, the flow passage 511i side.
As described above, leakage of the fluid R to the flow passage 511i side in the flow passage K prevents a liquid from being fed at a sufficient pressure to the inside of the subject via the flow passage 505i. 
A case where supply of the liquid E from the syringe 590 to the flow passage 505i via the fitting 530 varies the pressure on the downstream side relative to the first valve 551 in the flow passages 501i and 505i and the first valve 551 thereby unintentionally opens the flow passage 501i has been described above with reference to FIGS. 12 to 14.
Note that as another case where the pressure on the downstream side relative to the first valve 551 in the flow passages 501i and 505i varies, first, a case where the second valve 552 is intermittently depressed a plurality of times to intermittently perform a suction operation a plurality of times via the flow passage 505i and the flow passage V using the suction apparatus 533 may be contemplated.
Also, a situation immediately after completion of a suction operation via the flow passage 505i and the flow passage V using the suction apparatus 533, which is performed as a result of the second valve 552 being depressed, may be contemplated.
Furthermore, a case where during observation of the inside of the subject by insertion of the insertion portion of the endoscope into the inside of the subject, the pressure on the downstream side relative to the first valve 551 in the flow passages 505i and 501i, which are in communication with the inside of the subject, decreases for some reason may be contemplated.
Accordingly, there has been a demand for a configuration that can reliably prevent reverse flow of the fluid R to the flow passage 511i. 